The career of one of the titans of British industry came to a dramatic end yesterday when Lord Browne quit as chief executive of BP after lying to a court about his relationship with another man.

Following crisis talks at the company's London headquarters, BP said Lord Browne had resigned with immediate effect after losing his four-month battle to suppress newspaper reports about the relationship. In doing so, he forfeited a leaving package worth up to £15.5m.

Lord Browne went all the way to the House of Lords in his attempts to prevent Associated Newspapers, the publisher of the Mail on Sunday, from disclosing details of his relationship with Jeff Chevalier, his Canadian partner between 2002 and 2006.

A series of hearings considered evidence about the pair's extravagant international lifestyle, disputed allegations that company resources were diverted for Mr Chevalier's use, and claims - firmly denied - that Lord Browne attempted to evade tax payments.

The 58-year-old, once hailed as "the Sun King of the oil industry" lost his case, in large part, because he claimed to have met his partner while jogging in a London park. They had, his close associates conceded last night, made contact through a male escort agency's website.

In a statement which marked the end of a remarkable career, including a decade during which the company he led was regarded as the country's most successful, Lord Browne said: "In my 41 years with BP I have kept my private life separate from my business life. I have always regarded my sexuality as a personal matter, to be kept private. It is a matter of deep disappointment that a newspaper group has now decided that allegations about my personal life should be made public.

"I wish to acknowledge that I did have a four-year relationship with Jeff Chevalier, who has now chosen to tell his story to Associated Newspapers. These allegations are full of misleading and erroneous claims. In particular, I deny categorically any allegations of improper conduct relating to BP."

Tony Hayward, Lord Browne's designated successor, who had been due to take over in July, was immediately appointed as chief executive.

The disclosure of the relationship follows the refusal by the House of Lords yesterday to grant Lord Browne permission to appeal against rulings made earlier this year by the high court and court of appeal.

The high court had decided to lift an injunction which covered a wide range of subjects, including alleged discussions between Lord Browne and Gordon Brown, Tony Blair and EU commissioner Peter Mandelson, and a dinner at one of Lord Browne's homes attended by himself and Mr Chevalier with Mr Mandelson and his Brazilian partner.

Another was a claim that Lord Browne bought a flat in Venice several years ago and, it was alleged, paid cash for a renovation bill which did not include VAT, and that he failed to pay his tax bill.

The court also heard that Lord Browne took steps to enable Mr Chevalier to remain in the UK when his visa was due to run out early in the relationship. This included paying for a university course from 2003, so he would acquire student status, and helping him to set up a company to trade in mobile phone ring tones.

Mr Chevalier claimed that when the relationship broke down Lord Browne had agreed that "if needed, [he] would assist in the first year of me transitioning from living in multimillion pound homes around the world, flying in private jets, five-star hotels, £2,000 suits, and so on to a less than modest life in Canada".

The judge, Mr Justice Eady, said Mr Chevalier sought further assistance towards the end of last year, backed by what he said could be interpreted as a "thinly-veiled threat". Mr Chevalier denies making any threats.

Eventually, Lord Browne's attempts to prevent reporting of these matters, and to maintain his personal privacy, collapsed after the court accepted he had lied to conceal the manner in which he met Mr Chevalier. Lord Browne had told the court on more than one occasion that they had met while running in Battersea Park, south London. In fact, associates of Lord Browne now acknowledge, they met through a website called suitedandbooted.com.

Mr Justice Eady said: "I am not prepared to make allowances for a 'white lie' told to the court in circumstances such as these - especially by a man who prays in aid of his reputation and distinction, and refers to the various honours he has received under the present government, when asking the court to prefer his account of what took place."

The judge added that Lord Browne told this lie at a time when he was also making a "wholesale attack" on Mr Chevalier's reliability, showing a "willingness casually to 'trash' the reputation" of his former partner.

The Mail on Sunday said it would make its evidence available to the attorney general, Lord Goldsmith. "Jeffrey Archer and Jonathan Aitken went to prison for lying to the courts," a spokesman said.

However, Mr Justice Eady said he had decided not to refer the matter to the attorney general, saying disclosure in the judgment of Lord Browne's behaviour was "probably sufficient punishment".

In a statement last night the Mail on Sunday said: "The story we originally sought to publish was a business story involving issues of great importance to shareholders and employers of BP. Lord Browne chose to suppress this story by arguing to the high court that, because the story was supplied to us by his former lover, Mr Chevalier, it breached his right to a private life under the Human Rights Act." In lying, the newspaper said, it was Lord Browne who had made his private life a public issue.